A visual stumulus produces a large number of discrete points of stimulation on the receptor layer of the retina. The input is constantly changing, yet humans make sense out of this infinitely varying flux. Theories of how humans make sense out of a patterned visual input usually include two broad classes of operations--encoding and interpretation. Encoding is thought to involve the abstraction of features in a pattern. Interpretative operations are thought to take the results of this feature coding and figure out what the pattern is. It is not clear, however, what mechanisms are involved in each of these two classes, nor what mechanisms get the visual system from one class to the other. The basic approach is to apply to questions of encoding and interpretation some of the highly developed psychophysical techniques that have usually been thought applicable only to simple feature- selectivity or to peripheral sensory process. With these techniques, I am exploring the following questions. How are elementary features extracted and represented? In what ways are the initial representatives transformed, and what are the rules of transformation? In what kinds of interpretative processes are initial representations involved? What are the various ways in which patterns and interpretations of patterns are internally represented? The long-range goal of this project is to find out how humans make pictures out of punctate stimulation by characterizing in detail two fundamental processes involved in pattern recognition: encoding and interpretation. Bibliographic references: Tangney, J., Berbaum, K., and Weisstein, N. Masking independent of both separation and frequency: Implications for a Fourier approach. Abstract, Association for Research in Vision and Ophthalmology. Sarasota, Florida, 1975. Weisstein, N., Matthews, M., & Berbaum, K. Illusory contours can mask real contours. Abstract, Psychonomic Society, Boston, 1974.